Calcium is one of the more common elements found in both nature and many manufactured, by-product and waste substances. Its removal or recovery from such substances is often a key process step or requirement in upgrading, recovering or recycling the mixture or compound containing the calcium, or a key step in recovering the calcium in a form such as lime (CaO), which is the main calcium product of commerce.
Present methods of calcium separation from other substances are mainly based on the relative insolubility of calcium sulfate. The recovery and separation of calcium as calcium sulfate has high costs and several limitations. Not only must a source of sulfate, such as sulfuric acid, be acquired, and utilized, but the ultimate product, calcium sulfate, represents a much lesser value when compared to calcium in the form of lime, as calcium sulfate has only very limited markets.